property_value -n $GLOBAL['CACHE'] is available only in global context (xdebug_break(); // 2). The command will be responced by "can not get property" if it was called from function (xdebug_break(); // 1).

There is indeed a bug, or rather, something that is not implemented. The property_value implementation misses support for -c, so it doesn't use the superglobals context. This should be an easy fix though.